In conventional audio encoding/decoding algorithms, more quantization noises are introduced in an output signal due to an inaccurate quantization process in a case that the number of bits is small.
For example, in Adaptive Differential Pulse Code Modulation (ADPCM) encoding, if a very small number of bits is allocated to each sample point, too many quantization noises are introduced in the output signal due to an excessively high quantization error. Alternatively, in band spreading, generally only envelope information of some frequency spectra is transferred from an encoder to a decoder due to limitation of the number of bits, and a fine structure is generally obtained from a frequency spectrum of a low band. Although low-frequency fine structure and high-frequency fine structure have a certain correlation, some differences still exist. Therefore, the output signal obtained through a band spreading algorithm generally has some noises. Alternatively, due to limitations of other algorithms, some man-made noises are also introduced in the output signal.
In order to solve the foregoing problems, an encoding/decoding algorithm is proposed in the prior art, which has a main principle of performing post-processing on a frequency-domain signal according to a Signal-to-Noise Ratio (SNR) of the signal. The algorithm in the prior art has some effects on removal of noises among harmonic signals when a frequency-domain resolution is high, and can also make the frequency spectra of non-harmonic signals become flat.
However, in the implementation of the present invention, the inventors find that the prior art has at least the following problems:
As the post-processing of the frequency-domain signal is performed according to the SNR of the signal in the prior art, the output signal processed by using the algorithm in the prior art still has the problem of great noises.